Process and material for masking in color correction



Oct. 15, 1940. B. H. CARROLL AL 2 ,218,229

PROCESS AND MATERIAL FOR MASKING IN COLOR CORRECTION Filed March 31, 193'! Fig]. 2.

EXPOSED-YELLOW FILTER IMAGE RED SENSITIYEQ (a? GREEN sE-smvE- 1 E F, l I

/ pEvEwPED I l i I DEVELOPED EXPSED-NO FILTER 25w NEGATIVE IMAGE GREEH POSITIVE IMAGE (YELLOW Z I DEVELOPED 9 INVENTORS:

BY m.m @JMM ATTORNEYS:

IMAGE .2 densities.

Patented Oct. 15, 1940 PATENT OFFICE PROCESS AND MATERIAL FOR MASKING IN COLOR CORRECTION Burt H. Carroll and Cyril J. Stand, Rochester,

N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application March 31, 1937, Serial No. 134,118

1 Claim.

This invention'relates to photographic reproduction and particularly to methods and materials 'useful in the graphic arts for reproduction of colored objects and natural colored scenes.

5 In the reproduction of colored objects and natural colored scenes pigments or inks are used which do not absorb and transmit light in the correct spectral regions. In order to overcome these deficiencies of the printing pigments or inks 0 two general methods are in use. The first method involves a mechanical correction of the printing plates by means of hand retouching in order to render the result more nearly representative of the original'subject. According to the second 15 method of correcting for deficiencies in the pigments and inks, positive masks are used to print the corrected plates for certain of the color separations and a correction is thereby obtained photographically by a subtraction of photographic In the masking method of color correction, it is necessary to secure exact registration of the masks with the corresponding negatives so a that an accurate print can be made. A process of this typeis described, for example, in a book 25 entitled The Modern Masking Method of Correct Color Reproduction published by the Eastman Kodak Company, Rochester, New York in 1936. The necessity for registering the masks in this method of color correction haslimited its utility.

It is, accordingly, an object of the present invention to provide a'simpler masking method which obviates the necessity of registration of the masks. A further object is to provide an integral mask and a method of formingimages 35 therein.

These objects are accomplished by making use of a novel photographic element in which the sensitive layer designed to record the maskingv image is integral with the sensitive layer designed 40 to record the'color separation image. These laya ers arethen processed by some means .which produces a negative image of the color separation record and a positive image of the mask.

In the accompanying drawing,

vention.

Figs. 2, 4 and 6 are enlarged sectional views of the corresponding elements after formation of 50 images therein.

The essential feature of the masking process now in useis the printing of corrected positives Q Figs. 1, 3 and 5 are enlarged sectional views of photographic elements used according to our in-v by the use of masking positives placed in registry with one or more of the separation negatives during printing. The choice of the separation negatives which are to be corrected depends on thetransmission and reflection characteristics of the 5 printing inks. With inks available at present, it its generally desirable to correct the magentaand the yellow printing negatives, that is, the negatives made through the green and the blue filters, respectively. The blue-green negative made 10 through the red filter usually does not need to be corrected. The general procedure is to correct the magenta printing negative with a 'mask which is a weak positive printed from the bluegreen negative (made throughthe red filter), and

to correct the yellow printing negative with a mask which is a weak positive made from the magenta negative (made through the green filter).- However, a negative made by light corresponding to any of the three tri-color filters may, be masked by a positive made by a light corresponding to eitherof the other two. I

Our general procedure is to use a photographic plate or film provided with two layers of emulsion having different spectral sensitivities, one coated over the other so that the images formed in the two layers are permanently in register. The two layers may or may not be separated by a gelatin inter-layer. Such inter-layers at present may be dyed to act as filters or one of the layers of '30 emulsion may be dyed. One of the emulsions will be developed to a normal negative, andthe other emulsion will be converted to a positive by suitable means. The emulsion which is developed to a negative will be the more sensitive or will 5 have higher contrast as the masking positive will always be weaker than the negative. Various techniques may be employed in the processing of the sensitiveelement. One method I of securing differential treatment of the layers is 40 to employ means for controlling the diffusion of the processing baths, so that the actionof the baths is limited to the outer sensitive layer. In this case, an emulsion layer which is to recordthe negative image is coated next to the support and posure bothemulsions aredeveloped, but not fixed. After washing to remove the developer,

the silver image in the upper layer is removed by a suitable bleach bath, such as a mixture of quinone and hydrochloric acid in isopropyl alcohol containing small mounts of water. By controlling the time ofaction oi: bath and the concentration of water in the solution, it is possible to convert the image in the upper layer to silver chloride without affecting the lower layer. The silver chloride may then be removed by treatment with a sodium sulfite solution, which may be saturated with dissolved silver bromide to prevent attack on the unexposed silver bromide. The plate or film is then fogged and the upper layer only is developed by using a developer, the diffusion of which may be controlled, for example, by means similar to that used in the bleach bath. A developer of this type is, for example, a solution of 1:2:4-trihydroxybenzene, triethylamine and sodium sulfite in isopmpyl alcohol containing a small amount of water." Aiterdevelopment oi the upper layer to a positive, followed by treatment in an acid stop bath, the plate may be fixed in the usual mannefi In'an alternativemethod involving the use of means to control the penetration of. the treating baths a silver chloride emulsion is used for the lowerlayer. A slow fine-grain silver bromide emulsion is coated over this with or without a gelatin interlayer. In this case. after development in the usual way, the upper layer is treated with the quinone and hydrochloric acid bleach bath described above to convert the image in the V upper layer only, to silver chloride. The film is then treated with a sodium sulfite solution which removes not only the silver chloride formed in the upper layer by bleaching, but also the undeveloped silver chloride 01 the lower layer. After washing, the undeveloped silver bromide of the upper layer may then be;developed to a positive by any standard developer. A second method of forming a positive imag in only one of the layers is by bleaching a uniiormly colored gelatin layer in the immediate vicinity of a silver image. The layer which is to record the positive image is uniformly dyed with dye absorbing the light to be used in printing, for example, a yellow dye. After exposure both layers will be developed to negatives and the plate or film fixedmnd washed, it will be then treated with a suitable bleaching bath, such as an acid solution of thiourea. The dye will be bleached in contact with the silver image in the dyed layer and, by suitable choice of dye and silver concentrations in this layer, the decrease in density caused by bleaching oi the dye may be made to exceed the density of the silver, so

that an efiective positive image results for printing.

A third method of obtaining a positive image in only one is 'to employ an emulsion for one of the layers which gives a positive by solarization. tively low, but may be sumcient to be combined with a low sensitivity printing material where it is desired to obtain a corrected negative iroma colored positive original.

Our invention will now be described by particular reference to the accompanying drawing. The

drawing illustrates in Figs. 1 to 4 methods of processing, involving the use of differential diffusion and in Figs. 5 and 6 a method involving transparent material, such as glass or cellulose esters, is coated with a green sensitive emulsion layer H and a red-sensitive emulsion layer i2.

The sensitivity of such layers is rela- A thin gelatin layer may be interposed in the sensitive layers, but this is not absolutely necessary. The emulsion from which the layer H is formed is an emulsion which gives the usual amount of contrast and which may be developed emulsion from which layer I2 is formed is of a type which gives low contrast and should give a density range oi about of that of the emulsion oi layer 1 I.

The element is exposed to a colored object or a natural colored scene through a yellow filter which prevents action of blue light on the sensitive layers. The green component of the colored object or scene is recorded in layer II and the red component is recorded in layer l2. The plate or film is then developed by one of the controldiilusion methods described above to form a negative image l3 in the lower layer and a positive image It in the upper layer, as shown in Fig. 2. The plate or film formed in this way may then be used to print a corrected positive which is used in preparing the magenta printing plate.

As shown in Fig. 3, an element may be used which comprises a transparent support It coated with a blue-sensitive layer l5 and a green-sensitive layer IS. A yellow filter layer 11 is interposed between layers l5 and I8. This element is exposed irom the support side to the colored object or natural colored scene to record the blue component of the object or scene in emulsion layer I 5 and the green component in emulsion layer It. The filter layer I'I prevents blue light from afiecting the layer ll. Aiterdevelopment of the plate or film by one of the controlled diflusion methods described, a silver negative image I! is formed in the lowerlayer and a silver positive to a density range of slightly over one. The,

image IS in the upper layers. As shown at Ill,

the yellow dye or filter layer I1 is removed during the processing, with or without the use of a separate bath.

As shown in Fig. 5, the support II is coated with an emulsion layer 2| containing a yellow dye uniformly dispersed throughout the layer. Over this is coated a plain gelatin layer 22 iollowed by a blue-sensitive layer 23. The yellow dyed layer 2| is sensitive to green light. This element is exposed from the emulsion side without making use of a special filter to record the blue component of a colored object or scene in layer ll and the green component of the object or scene in layer 2!.

The plate or film is developed, fixed and washed and is then treated in a suitable bleaching bath, such as an acid solution 01 thiourea. which bleaches the yellow dye of layer Il-at the points adjacent the silver image. As shown in Fig. 6,

this leaves a positive dye image 24 in the lower layer and a negative silver image 25 in the upper layer. This element may be printed with blue light to give a corrected color separation positive.

The positives printed from the elements of Figs. 4 or 6 are used to make the yellow printing plate. The following examples, which are by way of illustration only, indicate methods of forming the corrected elements according to our invention.

Example I A plate or film is coated with a negative emulsion sensitized iongreen light with a dye, such as 2:1'-diethyl-3:4-benzthla-2'-cyanine bromide. Over this is coated a thin layer of gelatin, followed by a thin layer of a low contrastemulsion sensitized primarily to red iight with a dye, such ment is exposed through a yellow filter which -absorbs blue light, then developed throughout Glycerine cubic centimeters 500 Isopropyl alcohol do 1,000 Quinone grams 5 HCl "cubic centimeters" 50 Time of action of this bath is controlled so that only the upper layer of emulsion is bleached; its

action is stopped at this point by the use of a stop bath, which may be of the following composition:

Sodium bisulfite grams 3o. Isopropyl alcohol cubic centlmeters 1,000 Glycerine dn 1,000 Water -4 do 1,000 After the stop bath, the plate is washed. The

silver chloride which has formed by action of the bleach bath is removed by use of a sodium sulfite solution containing silver bromide to reduce its attack on the remaining silver bromide; the formula is, for example:

Following this, the plate is washed and preferably dried. The plate is then exposed to fog it uni formly. The upper layer onlyis then developed by controlled diii'usion of a developer which may be of the following composition:

A. Isopropyl alcoho1 cubic centimeters 500 Hydroxy hydroquinonegrams 4 p-phenylene diamine do 0.25 B. Water do 200 Sodium sulfite do 10 Glycerine cubic centimeters 300 C. Triethyl amine do 10 The components are added to make-sol tions A and B. B is poured into A and C is a ded im- 1 'mediately before using; The plate is then washed and finally fixed to remove the unexposed AgBr in the lower layer and washed in the usual manner. There is thus obtained a negative made by green light and a positive made by red light. By printing this combination simultaneously on a sensitive emulsion layer, a corrected positive suitable for making the magenta printing plate may be obtained.

I Example]! A plate or film is coated with a silver chloride emulsion sensitized to green light. Over this is coated a thin gelatin layer followed by a relatively slow fi rain silver bromide emulsion sensitized prima y to red light. This element is exposed through a yellow filter and developed in chloride in both layers. The plate is then washed and the remaining silver bromide in the upper layer is developed to a positive image by any standard developer, such as the following:

- as 2,2"-diethyloxadicarbocyanine iodide. The ele- Monomethyl-p-aminophenol sulfate grams 1.0 NazSOa do 75.0 Hydroquinone do.. 9.0 NazCOs do 25.0 KBr do 5.0

Waterton cubic centimeters 1000.0

- Example III An unsensitized emulsion sensitive to blue and violet light only is coated on a plate or film support. Over this is coated a layer of gelatin containing a non-diflusing yellow dye, such as chrysophenine (Schultz Farbstoii'tabellen 7th edition, No. 726). Over this layeris coated a layer of green-sensitive, low-contrast emulsion. The combination is exposed through the support without a filter. After exposure, the lower layer is developed to a. negative and the upper layer is reversed by controlled diffusion to a positive. Afterfixing, the yellow dye is removed by an appropriate bath, such as sodium hydrosulflte. A corrected negative is thereby obtained for making the yellow printing plate of any of the usual photo-mechanical printing processes.

, Example IV without a filter, the element is developed and fixed in the usual way. It is then treated with an acid solution of thiourea of the following composition:

Thiourea grams;

7.0 Sulfuric acid (93%) cubic centimeters 0.5 Hydroquinone grams 3.0 Chrome alum d0 5.0 Water c ubic centimeters 200.0

This solution bleaches the dye in the lower layer differentially where the silver image is present.

The element may then be printed with blue light to form a corrected positive representing the yellowprinting fplate.

As 'analternative method,.the lower emulsion layer may be dyed with Vat Yellow R (du Pont) which is then bleached on processing by treatment in an alkaline sodium stannite' solution of the following composition; I

SnClz-2H2O grams 8 Water to cubic centimeters To this add NaOH solution, 100 g. per liter, 100

cc. v To this add 2.5 mg. anthraquinone 10 cc. triethanolamine. I It is to be understood that other methods of procedure may be employed-according to our inthe ordinary way. The image in the upper layercomprises forming in the layer not containing thedye a negative metallic silver image representing one of the primary color components of a colored object, forming in the layer containing the dye a negative metallic silver image representing another primary color component 01' the colored object, bleaching the dye in the region of the last-mentioned negative image to form a positive dye image serving as a masking image and printing through the two images simultaneously with light of a color substantially complementary to the color positive dye image to form a corrected color component image representing the color complementary to that represented by the negative image.

BURT H. CARROLL. CYRIL J. STAUD. 

